Musical instrument and piezoelectric pickup with diaphragms and inertial mass



Nov. 3, 1970 J. s, BACHTK; ETALl 3,538,232

MUSICAL INSTRUMENT AND PIEZOELECTRIC PICKUP WITH DIAPHRAGMS AND INERTIALMASS Filed Aug. l2, 1968 3 Sheets-Sheet 1 32d. Zz vZ5 /Z 32a. 55' 3 7 IE. .4 WAM/AMA wwf/iff dmc/d5 .fria/ffm Nov. 3, 1970 J. s. BACI-ms ETAI-3,538,232

MUSICAL INSTRUMENT AND PIEZOELECTRIC PICKUP WITH DIAPHRAGMS AND INERTIALMASS Filed Aug. 12. 1968 l l5 Sheets-Sheet 2 v INVENTORS ./dfP/f 5.Ac/V774 United States Patent O `U.S. Cl. 84-1.14 10 Claims `ABSTRACT OFTHE DISCLOSURE An inertia type pickup device for utilization inconjunction with a musical instrument, such as a guitar. The pickupdevice is of the piezoelectric type and includes a piezoelectric elementcentrally retained between a pair of diaphragms. The diaphragms havetheir peripheries supported by the rigid housing of the device. A weightis attached to the center of one of the diaphragms to 'increase the massinertia of the transducer system. When subjected to a vibration inputthe peripheries of the diaphragms moverela'tive to their centers,causing flexure of the piezoelectric element and production ofelectrical signals corresponding to the mechanical vibrations. Thedevice may be simply attached to the musical instrument by adouble-faced adhesive member.

BACKGROUND OF THE INVENTION This invention relates to transducers andmore particularly relates to transducers for use with musicalinstruments to provide electrical amplification of the vibrationaccompanying the sound produced by these instruments.

Typical electrical amplification systems for use with musicalinstruments such as guitars, violins, pianos, etc., include theinstrument, a pickup device for converting the mechanical vibrationsfrom the instrument, an electrical signal, an electrical amplifier foramplifying the electrical signals and a loud speaker for converting theamplified electrical signal to acoustic energy. It is noted that whilethe instant invention will be described with reference to a guitarsystem, this invention may be used with numerous other musicalinstruments having suitable vibratile members as will be apparent tothose of ordinary skill in the art.

In musical systems of the above type and especially where the musicalinstrument is a guitar or violin, it is of great advantage to provideversatility of the instrument so that it may be used both with andwithout electrical amplification. It is also of advantage to be able tovary the location on an instrument of a transducer, when the instrumentis used with an electrical amplifier, so that it may be positionedasbest suits the individual. These qualities have not been attainable bythe prior art without great sacrifice in the fidelity of electricalamplification.

Previous types of pickup devices for providing electrical amplificationof the soundof a musical instrument have included such devices asmicrophones, magnetic type pickups, piezoelectric devices andcapacitance type devices. Each of the above pickups has suffereddrawbacks of one kind or another.

The use of microphones for electrically amplifying the sound of amusical instrument has proved undesirable in many situations.Microphones have a great susceptibility to pickup extraneous sounds andechoes and amplify them with the music to be amplified. As a result thequality of the sound is often poor. In addition, there is a tendency forthe amplified music to be fed back through the microphones producingoscillations (squeal).

The magnetic type devices usually consist of a magnetic coil which picksup the vibrations of the steel strings of a guitar. Such pickups,however, are unsuitable where the strings are other than steel. Inaddition, these pickups are also very susceptible to extraneousinterference from stray electromagnetic fields.

Previous piezoelectric and capacitance type transducers have also hadtheir drawbacks. In particular, the mechanical characteristics of theprevious transducers of these types are such that they required secureand permanent affixing to a vibratile member of the musical instrumentin order to produce electrical oscillations precisely corresponding tothe mechanical vibrations. These transducers were usually secured to amusical instrument such as the guitar at the bridge of the instrument,for direct actuation by the strings of the instrument. In addition, inorder to obtain the greatest fidelity, it was necessary to eliminate thesound box of the instrument to prevent the vibrations of the sound boxfrom affecting the piezoelectric or capacitance transducers. As a resultof the characteristics of the previous transducers of these types, theversatility of the instruments on which they were used was limited sincean instrument Without a sound box could only be used in combination withan electrical amplifier. In addition, the location of the transducers atthe bridge of the instrument limited access to these transducers formaintenance purposes. The fixed location of the transducers also made itimpossible for the individual to adjust the location upon the instrumentof the connection cable from the electrical amplifier accoring to hispersonal desires and comfort, or for best musical effect.

One method of apparently eliminating some of the disadvantages of theprevious transducers mentioned above would be to provide the transducerswith suitable securing means such as adhesive backing whereby thetransducer could be placed at any position on the instrument withoutpermanent fastening and damaging of the instrument. Thereby, thetransducer may be moved to any desired position comfortable and/orpleasing to the individual user of the instrument. This method has notbeen successfully employed with prior transducers because of the failureof such securing means to provide suitable mechanical coupling betweenthe vibratable member of the instrument and the vibration responsiveelements of the transducer. In particular, the adhesive backing acts asa damper and is not capable of providing the rigid mechanical couplingnecessary to cause the vibration of conventional transducer elements soas to produce electrical oscillations in correspondence to themechanical vibrations of the musical instrument. As a result, use ofsuch adhesive backing with the previously existing transducer produces avery poor quality music amplification.

The instant invention overcomes the above problems existing in the fieldof electrical amplification for musical instruments. In the illustratedpreferred embodiment of the invention, a novel reaction-typepiezoelectric transducer is provided with inertial reaction meansenabling the securement of the transducer to a musical instrument bymeans of an adhesive backing on the transducer while insuring highfidelity electrical amplification of the music. The transducer deviceconsists generally of a piezoelectric element or transducer membercarried along va vibratory portion of a diaphragm plate and having aweight of substantial inertia attached thereto. The weight operatesV asan inertia-reaction body resisting mechanical vibrations relative to theremoter portions of its supporting plate which are affixed to thehousing. The housing also carries a biasing structure, for instance, 4afurther vibratory plate, which has biasing elements such as a ridge orseveral protrusions, which enga'ge portions of the piezoelectrictransducer with a stressing force and subjects it to strainscorresponding to the housing vibrations thereby causing it" to deliver acorresponding electric signal output, as is known to the art. Bothvibratory plates are electrically conductive and provide electricalcontacts to the opposite sides of the piezoelectric element. An exteriorsurface of the transducer device may include an adhesive surface forafxing the transducer to a vibratory wall surface of a musicalinstrument.

It is, therefore, one object of the instant invention to provide atransducer lwhich may be readily secured to a musical instrument, suchas a guitar.

Another object of the instant invention is to provide a transducer whichmay be attached to a musical instrument without damaging the musicalinstrument and without leaving any permanent holes or attachments to themusical instrument.

A further object of the instant invention is to provide an improvedtransducer device of the piezoelectric type which operates on theinertial reaction principle.

An additional object of the instant invention is to provide such apiezoelectric transducer device which may be easily secured to a musicalinstrument as by an adhesive backed member or clamp.

Still another object of the invention is to provide a piezoelectrictransducer` device having a piezoelectric element retained between apair of vibratory plates, which are responsive to mechanical vibrationsto iiex the piezoelectric element thereby causing the production ofelectrical signals corresponding in amplitude and frequency to themechanical vibrations.

The aforementioned objects and features, along with additional objectsand features of the instant invention will become apparent from areading of the description of the invention in conjunction with thedrawings, as follows:

FIG. l is a perspective view of an electric guitar system with theinstant invention incorporated therein;

FIG. 2 is an exploded perspective view of the pickup device of theinstant invention;

FIG. 3 is a plan view of the pickup device of the instant invention withits housing cover removed;

FIG. 4 is a cross-sectional view of the pickup device of the instantinvention taken along line 3 3 of FIG. 2, and including the housingcover;

FIG. 5 is an enlarged partial View of the diaphragm and transducerassembly of the pickup device of the instant invention in the vicinityof the piezoelectric armature and weight; and

FIG. 6 is a perspective view of the housing removed from its metalshell;

FIG. 7 is a perspective view of the housing cover showing the undersidewhich mates with the housing when the cover is secured to the housing.

Referring first to FIG. 1, there is shown a musical system including aguitar 1, amplifier 6 and a loudspeaker 5. The system further includesthe transducer device 2 of the instant invention on the vibratorysounding board 3 of the guitar 1. The transducer device 2 converts thevibratory motion of the guitar to an electrical signal forpresentment'to amplifier 6. The transducer device 2 is thereforeconnected by an electric cable 4 to a suitable audio amplifier 6generally shown. The output of amplifier 6y isin turn, connected to theloudspeaker 5 by means of electriccable 7. The electrical circuitry ofthe amplifier and loud speaker circuit are not shown in detail sincethey form no part of the instant invention and may consist of. typicalcircuitry well known in the art for use with piezoelectric transducers.It is to be understood that while the instrument shown in FIG. l is aguitar, and while the transducer device is located on the sounding boardof the guitar, the transducer device of the instant invention vmay beused on a variety of musical instruments and it may be located at anyone of a number of suitable locations onthe instruments, as will beapparent t0 those skilled in the art.

Referring now to FIGS. 2 through 7, transducer@ includes external casingmembers30` and 37 heldptogether by screw means 38 or other appropriatesecurement means. The internal region of main housing section 30includes a cylindrical cavity opening 31 bounded by ridge 33. Cavity 31includes a diaphragm assembly of thin conductive plates 11, 12,sandwichingbetween'them a thin square shaped piezoelectric elementortransducer member 14. The transducer 14 which generatesa voltageoutput corresponding to the imposed mechanical 'strain may be any typeof known piezoelectric or piezoresistive material. It is shown as a thinpiezoelectric planar member having a square shape-However, otherconfigurations may be utilized (esg. circular or4 rectangular).Transducer 14 may typically be a bilaminate and has two outer exteriormetallic electrode surfaces for electrical connection to the externalcircuits. These opposed electrode surfaces are in good electricalengagement with the metallic diaphragm for providing the externalcircuit connection (via 21, 22).

The piezoelectric transducer 14 is seated within the square cutoutsection 13A of the lesser thickness insulating spacer 13. The insulatorsheet 13 is coextensive with the two diaphragm plates 11, 12 and may beof polyethylene or other suitable plastic sheet material. The plates 11and 12 and the insulator 13 are concentric with the piezoelectrictransducer 14. As can be seen clearly in FIG. 5, the diaphragm plate 12has protruding straining means shown, for example, as an annulardepression 15 which engages the corner portions along the upper surface14 of the square piezoelectric transducer disc 14 for imparting theretostrains corresponding to the vibrations imparted to the main casingmember 37. Alternatively, -annular protrusion 15 may be replaced with aplurality of appropriately positioned dimples. This straining meansprestresses the diaphragm plates 11 and 12 and the piezoelectrictransducer member 14 to assure that the piezoelectric transducer member14 is forced to remain in substantial contact with nearby portions ofvibratory plates 11 and 12 while the peripheral portions of the plates11 and 12 move relative to its central portion in response to impartedmechanical vibrations.

A member or weight 16, having substantial mass or inertia is connectedto the intermediate vibratory mass of the diaphragm assembly. The Weight16 is shown connected by a rivet 17, including an upturned region 19 incontact engagement with the central region of the lower 'transducersurface 14".

The plates 11 and 12 are connected to a pair of contact springs 21 and22, via ine conductor wires 23, 24, respectively. The two Contactsprings 21 and 22 have exposed terminal sections for connection to cable4 leading to the amplifier 6. The contact spring 22 may be connected tothe ground of the amplier circuit. Hence, a grouding strap 25 is alsoshown connected to diaphragm plate 12.

The diaphragm assembly above described is mounted in the interior cavity31 of the plastic or epoxy main housing fbody 30. The cavity 31 has asmaller diameter than the plates 11, 12, so that the peripheries ofplates 11, 12 and 13 rest upon underlying circular housing shoulder 32.The shoulder 32 is surrounded lby an upstanding wall 32a of the housing30, having a diameter substantially corresponding to the diameter of theplates 11 and 12. The housing member 30 has a passage 33 through whichthe grounding strap 25 passes and further includes housing passages 34and 35 in which the terminal spring contacts 21 and 22 are located.These housing passages 34, 35, lead to a common recess 36 for permittingthe insertion of av two-conductor plug (not shown) to make contact withthe spring contacts 21` and 22, respectively. f

As seen in FIGS. 4 and 7, the housinghas a complementary cover member,preferably constructed of the same material as housing member 30. Thecover 37 .has a circular shoulder 32b which will closely confronthoustween the peripheries .of the plates 11 and 12 and the housingsections 30, 37.

The bottom side of housing member 30 is surrounded :byay metal shell 39.This shell includes an opening 36' in registry with 36 for .permittingthe entrance of a plug forvvcontact with the contact springs 21 and 22.The housing 30 is secured within the metal shell 39 so as to lprovidegrounded-contact between the metal shell and the grounding strap 25 onplate 12. The grounding of I.the-'metal shell 39 and the plate 12 form acomplete electrical shield against extraneous electricalinterference:sincethe shell 39 and plate 12 completely surround the piezoelectrictransducer member 14 and the ungrounded plate 11.

' In operation, the transducer device of the instant invention is placedupon a vibratory wall of the musical instrument by a double facedadhesive member 38 (FIG. 4) of appropriate clamp. When .the instrumentis played, the housing 30 and its cover 37 vibrate with the musicalinstrument at substantially the same amplitude as the portion of theinstrument upon which the transducer device is secured. Since theperipheries of plates 11 and 12 are rigidly mounted on the housing ridge32, these peripheries also move as a result of the mechanicalvibrations. However, the relatively large mass provides by weight 16 atthe center of the vibrating plate 11 resists displacement because of itsinertial reaction to such movement. Since the piezoelectric transducermember 14 is biased against the plate 11 by the annular ridge 15, thepiezoelectric transducer member is flexed by the relative motion betweenthe central regions of plates 11 and 12. The periphery of plate 11 movesrelative to its center, thereby causing stresses and strains on thepiezoelectric transducer member 14 and these stresses and strains aretransduced to proportional voltages corresponding to the mechanicalvibrations. These voltages are then transmitted to the amplifier 6through plates 11 and 12 and contacts 21 and 22. The amplified signal isreconverted to acoustic energy by loudspeaker 5.

As can be seen from the above description of the instant invention, asmall compact inexpensive transducer is provided having the features ofbeing durable. rugged, and versatile, and at the same time providinghigh quality amplification for a musical instrument.

While the instant invention has been described with respect to onepreferred embodiment thereof, many modications and variations will nowbecome apparent to those skilled in the art. It is, therefore, preferredthat the scope of this invention not be limited by the specificdisclosure herein, but only by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. In an acoustic transducer device for electrically reproducing theacoustic output of a musical instrument having a vibratory instrumentwall,

an enclosure housing including a mounting portion for attachment to andvibration with the vibratory instrument wall;

said enclosure housing having an internal cavity containing two oppositevibratory diaphragms, both having their peripheral rims held by a nearbyrigid region of the housing, and

a mechanoelectric transducer plate for supplying an electrical signaloutput corresponding to motion strains imparted to said transducerplate,

said transducer plate held with its opposite extended planar surfacessandwiched between intermediate regions of said diaphragms, and radiallyspaced from said peripheral rims,

said transducer plate supported on the intermediate region of one ofsaid diaphragms, said one diaphragm having a predeterminedly selectedmotionresisting mass inertia for causing the central regions ofdiaphragms to undergo relative exure when subjected to vibrationsimparted to said housing mounting portion, imparting strains to saidtransducer plate and thereby supplying transducer signals correspondingto said imparted vibrations.

2. In an acoustic transducer as claimed in claim 1,

including additional mass means operatively connected to theintermediate position of said one diaphragm for correspondinglyincreasing said mass inertia and the signal output of said transducerplate.

3. In an acoustic transducer as claimed in claim 1,

said transducer plate having first and second opposite metallic surfaceelectrodes along its exposed opposite surfaces,

said two diaphragms having metallic contact surfaces engaging underpressure said first and second surface electrodes and providing firstand second external signal output connections from said transducerplate.

4. In an acoustic transducer las claimed in claim 1,

an insulating layer disposed between said two diaphragms and holdingsaid transducer plate between said opposite intermediate diaphragmregions.

5. In an acoustic transducer as claimed in claim 1,

the other of said diaphragms having at least one protrusion engagingunder predetermined pressure a certain region of said transducer plateand thereby causing such transducer plate to undergo strainscorresponding to flexure of said one diaphragm.

6. In an acoustic tran-sducer as claimed in claim 5,

said transducer plate having a square shape,

said protrusion of the other diaphragm being an annular depressionengaging `the far corner regions of said square shaped transducer plate.

7. In an acoustic transducer as claimed in claim 1,

lsaid one diaphragm engaging the central region of a first surface ofsaid transducer plate and the other of said diaphragm having at leastone protrusion engaging the peripheral portion of the opposed secondsurface of said transducer plate and thereby causing said transducerplate to undergo strains correspond- Iing to iiexure of said onediaphragm.

8. In an acoustic transducer as claimed in claim 7,

said other diaphragm having an lannular protrusion engagingsymmetrically said peripheral portion of said transducer plate secondsurface.

9. In an acoustic transducer as claimed in claim 3, further including,

an insulating member disposed between said two diaphragms and includinga central opening for snugly receiving said transducer plate andpositioning said transducer plate between said opposite intermediatediaphragm regions. p

10. 'In an acoustic transducer as claimed in claim 7,

`said transducer plate having first and second opposite metallic surfaceelectrodes along its exposed opposite surfaces,

said two diaphra-gms having metallic contact surfaces engaging underpressure said first and second surface electrodes and providing firstand second external signal output connections from said transducerplate,

including additional mass means operatively connected to theintermediate position of said one diaphragm for correspondinglyincreasing said mass inertia and the signal output of said transducerplate,

said additional mass means being a weight suspended from the surface ofsaid one diaphragm opposite said contact surface,

securing means for attaching said weight to the intermediate region ofsaid one diaphragm,

said securing means including a portion extending be- 8 yond saidcontact surface and providing Said central 3,460,061 8/ 19169 Massa310-8.4 X engagement with the transducer plate rst surface. 3,475,54310/'1969 Burns k 84451.16

References Cited WARREN E. RAY, Primary Examiner UNITED STATES PATENTS 5S. I. WITKOWSKI, Assistant Examiner 1,856,730 I5/1930 'Scherf 84-116 v3,030,735 3/1963 Evans 34-1.16 U-S-C1 X-R- 3,186,237 6/1965 Forrest31o-8,4 X 31o-8.4

